1. Undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities. 
2. Undesirable change in the physical, chemical, or biological characteristics of the air, water, or land that can harmfully affect the health, survival, or activities of human or other living organisms. 
3. Unwanted chemicals or other materials found in the air. Pollutants can harm health, the environment and property. Many air pollutants occur as gases or vapors, but some are very tiny solid particles: dust, smoke or soot. 
4. Any substances in water, soil, or air that degrade the natural quality of the environment, offend the senses of sight, taste, or smell, or cause a health hazard. The usefulness of the natural resource is usually impaired by the presence of pollutants and contaminants. 
5. Harm to a natural environment, such as air, water, or soil through contamination with either natural or human-made materials. Such contamination may be deliberate, accidental, direct, or indirect. Throwing garbage into the lake, for example, makes the water unhealthy for fish and unfit for humans to swim. Indirect pollutants can enter our water supply from groundwater and runoff that contain agricultural fertilizers and pesticides or improperly disposed of industrial waste. 
6. Pollution which is (1) induced by natural processes, including precipitation, seepage, percolation, and runoff; (2) not traceable to any discrete or identifiable facility; and (3) controllable through the utilization of wise management practices. 
7. The undesirable presence of matter or energy that can cause harmful environmental effects.
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